[PATCH AUTOSEL 6.0 11/11] powerpc/64: Fix msr_check_and_set/clear MSR[EE] race
From: Sasha Levin <sashal@kernel.org>
Date: 2022-10-14 13:52:58
Also in:
lkml, stable
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
From: Nicholas Piggin <npiggin@gmail.com> [ Upstream commit 0fa6831811f62cfc10415d731bcf9fde2647ad81 ] irq soft-masking means that when Linux irqs are disabled, the MSR[EE] value can change from 1 to 0 asynchronously: if a masked interrupt of the PACA_IRQ_MUST_HARD_MASK variety fires while irqs are disabled, the masked handler will return with MSR[EE]=0. This means a sequence like mtmsr(mfmsr() | MSR_FP) is racy if it can be called with local irqs disabled, unless a hard_irq_disable has been done. Reported-by: Sachin Sant <redacted> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221004051157.308999-2-npiggin@gmail.com (local) Signed-off-by: Sasha Levin <sashal@kernel.org> --- arch/powerpc/include/asm/hw_irq.h | 24 ++++++++++++++++++++++++ arch/powerpc/kernel/process.c | 4 ++-- 2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index 983551859891..9cb1daa1be4f 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h@@ -489,6 +489,30 @@ static inline void irq_soft_mask_regs_set_state(struct pt_regs *regs, unsigned l } #endif /* CONFIG_PPC64 */ +static inline unsigned long mtmsr_isync_irqsafe(unsigned long msr) +{ +#ifdef CONFIG_PPC64 + if (arch_irqs_disabled()) { + /* + * With soft-masking, MSR[EE] can change from 1 to 0 + * asynchronously when irqs are disabled, and we don't want to + * set MSR[EE] back to 1 here if that has happened. A race-free + * way to do this is ensure EE is already 0. Another way it + * could be done is with a RESTART_TABLE handler, but that's + * probably overkill here. + */ + msr &= ~MSR_EE; + mtmsr_isync(msr); + irq_soft_mask_set(IRQS_ALL_DISABLED); + local_paca->irq_happened |= PACA_IRQ_HARD_DIS; + } else +#endif + mtmsr_isync(msr); + + return msr; +} + + #define ARCH_IRQ_INIT_FLAGS IRQ_NOREQUEST #endif /* __ASSEMBLY__ */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 0fbda89cd1bb..37df0428e4fb 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c@@ -127,7 +127,7 @@ unsigned long notrace msr_check_and_set(unsigned long bits) newmsr |= MSR_VSX; if (oldmsr != newmsr) - mtmsr_isync(newmsr); + newmsr = mtmsr_isync_irqsafe(newmsr); return newmsr; }
@@ -145,7 +145,7 @@ void notrace __msr_check_and_clear(unsigned long bits) newmsr &= ~MSR_VSX; if (oldmsr != newmsr) - mtmsr_isync(newmsr); + mtmsr_isync_irqsafe(newmsr); } EXPORT_SYMBOL(__msr_check_and_clear);
--
2.35.1